The present invention relates to a wiring board with terminals for use in connecting circuits in a variety of electronic devices and a method for such a wiring board.
In recent years, flexible wiring boards are in wide use in a variety of electronic devices for connection between a plurality of circuit boards on which electronic components have been mounted, or for connecting a circuit board with a motor or circuit components and the like.
Referring to FIGS. 5 and 6, a description will be given on such a conventional wiring board with terminals. For easy understanding of the structure, drawings are shown with the dimension in the direction of the thickness expanded.
FIG. 5 is a partially sectional view of a conventional wiring board with terminals, and FIG. 6 is an exploded perspective view of a conventional wiring board with terminals. In the drawings, a plurality of wiring patterns 22 are formed by etching a thin film of a copper alloy and the like on the top surface of a film-like lower substrate 21 made of polyethylene terephthalate and the like having flexibility. Insulating layer 23 made of a polyester resin and the like covers the entire surface excluding connecting section 22A on both ends of wiring pattern 22. And, on the top surface of one end of connecting section 22A of lower substrate 21, terminal 25 is placed of which joining section 25A on one end is roughly T-shaped and which is made of a thin metal plate. Also, anisotropically-conductive adhesive 27 is coated on the bottom surface of film-like upper substrate 26 made of polyethylene terephthalate and the like. Adhesive 27 is prepared by dispersing in a rubber-based adhesive such as chloroprene rubber electrically conductive powders made by plating nickel or resin with a precious metal. A wiring board having such structure has been formed in the following manner. (1) Joining section 25A of terminal 25 made of a thin metal plate is placed on one end of connecting section 22A of lower substrate 21. (2) Upper substrate 26 is placed on connecting section 22A. (3) By pressing from the top surface of upper substrate 26 with heat, anisotropically-conductive adhesive 27 softens and solidifies thereby cementing lower substrate 21 and upper substrate 26 while sandwiching terminal 25.
A wiring board having above structure is installed in an electronic device. For example, lead wires of a motor and various elements are soldered to the end of terminal 25, and circuit boards are connected to connecting section 22A on the other end by means of a connector and the like. In this way, connection between a motor and the like and circuit boards are accomplished through terminal 25, conductive powder in anisotropically-conductive adhesive 27 and wiring pattern 22.
However, although such wiring board having terminals is superior in adhesion at room temperature, adhesive strength decreases when in use at elevated temperatures due to softening of anisotripically-conductive adhesive 27 thus lowering the holding power of terminal 25. The reason for this is because anisotropically-conductive adhesive 27 that cements terminal 25 comprises relatively low softening-temperature rubber such as chloroprene rubber of which the adhesion decreases at elevated temperatures.
In order to solve this problem, while two or more adhesive materials may be blended, the selection of materials is difficult as blending is difficult depending on the material combination, or materials are limited.
A wiring board with terminals is provided which is constructed by forming between an upper and a lower substrates two layers of adhesives that have different softening temperatures. And a method for manufacturing such a wiring board is provided.